The major objective of the proposed work is to study the functional organization of brain stem and spinal pathways mediating sympathetic and parasympathetic influences on the cardiovascular system of the cat. Problems related to this objective are approached primarily with single and multiunit electrophysiological recording techniques. The specific aims of the research are: 1) to study the organization of brain and spinal pressor regions; 2) to define the relationships between central pressor pathways and the baroreceptor reflex; 3) to define the relationships between central pressor pathways and the sympatho-inhibitory systems of the medial medulla and forebrain; 4) to define the relationships between brain stem vasomotor areas and single sympathetic preganglionic neurons of the intermedio-lateral cell columns of the spinal cord; 5) to define the sites within the brain stem and spinal sympathetic pathways at which depressant effects of centrally acting antihypertensive drugs are exerted; and 6) to define the brain stem sites and mechanisms involved in forebrain and respiratory modulation of the cardiac vagal component of the baroreceptor reflexes.